None of the following is admitted to be prior art to the present invention.
Webs and fabrics, especially those used to make garments and to make filters, could be vastly improved if there were a means to control the porosity or permeability of the web; although this fact has previously gone largely unrecognized. For example, a problem that has long plagued the art has been the inability to construct a rainwear garment that is waterproof, breathable and comfortable. Similarly, there is a great need for a medical gament that is breathable and comfortable but impermeable to disease causing microorganisms such as viruses and bacteria. What is needed is a single method of selectively controlling the porosity of a web that is capable of achieving any of a wide variety of desired porosities.
Articles having improved performance and functional properties are obtained at the expense of comfort and breathability. Greater comfort sacrifices maximum functionality and greater functionality sacrifices comfort However, conventional treatments of webs with silicone resins and fluorochemicals are typically unable to solve this dilemma and fall into the general categories of (i) surface coatings; (ii) saturations or impregnations; and (iii) layers of fibers and/or polymers.
I. Coatings
Prior fluorochemical and silicone (See U.S. Pat. Nos. 3,436,366; 3,639,155; 4,472,470; 4,500,584; and 4,666,765) fabric coating treatments evidently can protect only that side of the fabric upon which they are disposed. Such treatments significantly alter the hand, or tactile feel, of the treated side. Prior silicone fabric coatings typically degrade the tactile finish, or hand, of the fabric and give the coated fabric side a rubberized finish which is not appealing for many fabric uses, particularly garments.
Other polymeric coatings have been used in prior attempts to make a garment breathable, yet waterproof For example, U.S. Pat. No. 4,454,191 describes a waterproof and moisture-conducting fabric coated with a hydrophilic polymer. In addition, various polyorganosiloxane compositions can be used for making coatings that impart water-repellency to fabrics. For example, U.S. Pat. No. 4,370,365 describes such a product that is said to have a good "hand" and to possess waterproofness. However, it has not been shown that polyorganosiloxanes have been coated on fabrics in such a way that both high levels of resistance to water by the fibers/filaments and high levels of permeability to water vapor are achieved.
Porous webs have been further shown to be surface coated in, for example, U.S. Pat. Nos. 4,478,895; 4,112,179; 4,297,265; 2,893,962; 4,504,549; 3,360,394; 4,293,611; 4,472,470; and 4,666,765. These surface coatings impart various characteristics to the surface of a web, but remain on the surface and do not provide a film over the individual internal fibers and/or yarn bundles of the web. In addition, such coatings on the web surface tend to wash away quickly.
II. Saturation and Impregnation
Prior treatments of webs by saturation or impregnation with a polymer material, such as a silicone resin, are typically accomplished by immersion, using a low viscosity liquid silicone resin so that the low viscosity liquid can flow readily into the web, and be adsorbed or absorbed therewithin. Particularly for flexible webs, including fabric, an immersion application of a liquid or paste composition to the web is achieved, for example, by the so-called padding process wherein a fabric material is passed first through a bath and subsequently through squeeze rollers in the process sometimes called single-dip, single-nip padding. Alternatively, for example, the fabric can be passed between squeeze rollers, the bottom one of which carries the liquid or paste composition in a process sometimes called double-dip or double-nip padding.
The silicone resin treated product is typically a rubberized web, or fabric, that is very heavily impregnated with silicone. For example, U.S. Pat. No. 2,673,823 teaches impregnating a polymer into the interstices of a fabric and thus fully filling the interstices. Thus, this patent provides no control of the saturation of the fabric and instead teaches full saturation of the interstices of the fabric. Such a treated web is substantially devoid of its original tactile and visual properties, and instead has the characteristic rubbery properties of a cured silicone polymer.
Prior treatments of webs that force a composition into the spaces of the web while maintaining some breathability have relied on using low viscosity compositions or solvents to aid in the flow of the composition. U.S. Pat. No. 3,594,213 describes a process for impregnating or coating fabrics with liquified compositions to create a breathable fabric. Thus, the method of this patent imparts no energy into the composition to liquify it while forcing it into the spaces of the web, because the composition is substantially liquified before placement onto and into the web. U.S. Pat. No. 4,588,614 teaches a method for incorporating an active agent into a porous substrate. This process utilizes a solvent to aid in the incorporation of the active agent into the web. The active agent is a non-curable agent since the addition of heat aids in the reduction of viscosity.
III. Layers
Several references describe laminates or layers of fabrics and/or polymers. For example, U.S. Pat. Nos. 4,872,220; 5,024,594; 5,180,585; 5,335,372; and 5,391,423; describe articles that use layers of fabrics and/or polymers to protect against blood, microbes, and viruses from penetrating through the fabrics. Similarly, U.S. Pat. No. 4,991,232 describes a medical garment comprising a plurality of plies to prevent blood from penetrating through the garment.
IV. Additional Backround Information
One technique that does not easily fall within any of the three categories listed above (i.e., coatings, saturations, and layers) is described in Caldwell, American Dyes Reporter, 3:25-29, 1967 and U.S. Pat. No. 3,265,529, issued Aug. 9, 1966. These references describe a method for "coating" a fabric that mechanically pushes or forces a water swellable polymer below the surface of a fabric to form a discontinuous or porous layer that swells and forms a continous layer or barrier when contacted with water. It is said that an effective combination of comfort and rain protection was achieved. No indication is given that the polymer is thixotropic and it appears that the polymer does not substantially encapsulate the structural elements of the web.
The use of polytetrafluorethylene (PTFE) has been said to produce a fabric with a large plurality of pores of about 0.2 to 0.3 microns in contrast to conventional polyurethane coatings with pore sizes in the range of 2 to 3 microns. See U.S. Pat. No. 4,483,900, issued Nov. 20, 1984.
It has been said that the addition of a peroxide can lower the viscosity of polymer used as a barrier layer in a web laminate and provide a web having pore sizes distributed predominantly in the range of 7 to 12 microns, with a lesser amount of pores from 12 to 25 microns, with virtually no pores greater than 25 microns and with a peak of pore size distribution less than 10 microns. See U.S. Pat. No. 5,213,881, issued May 25, 1993.